While the utility of zeolite P in detergent formulations has been acknowledged, for example in European Patent Application 0384070 (Unilever), they must be manufactured by a commercially effective process in order to become available on the market place. Thus, while the properties of a material may make it a useful commercial commodity, its manufacture has to be optimised for large scale production. The zeolite P class includes a series of synthetic zeolite phases which may be in cubic configuration (also termed B or P.sub.c) or tetragonal configuration (also termed P.sub.1) but is not limited to these forms. The structure and characteristics of the zeolite P class are given in "Zeolite Molecular Sieves" of Donald W Breck (published 1974 and 1984 by Robert E Krieger of Florida USA). The zeolite P class has the typical oxide formula: EQU M.sub.2/n O.Al.sub.2 O.sub.3.2.0-5.00 SiO.sub.2.5H.sub.2 O.
M is an n-valent cation which for this invention is an alkali metal, that is lithium, potassium, sodium, caesium or rubidium with sodium and potassium being preferred and sodium being the cation normally used in commercial processes.
Thus sodium may be present as the major cation with another alkali metal present in a minor proportion to provide a specific benefit.
In EP-A-384,070 is disclosed a process for manufacturing zeolite P having a silicon to aluminium molar ratio not exceeding 1.33 wherein a sodium aluminate solution, having a Na.sub.2 O:Al.sub.2 O.sub.3 molar ratio from 1.4 to 2.0, is mixed with a sodium silicate solution, having a SiO.sub.2 :Na.sub.2 O molar ratio from 0.8 to 3.4, at a temperature from 25.degree. C. to boiling point and with vigorous stirring to give a gel having the following composition: EQU (2.3-7.5)Na.sub.2 O, (1.75-3.5)SiO.sub.2, Al.sub.2 O.sub.3, (80-450)H.sub.2 O.
The gel is then aged for 0.5 to 10 hours at a temperature above 70.degree. C., the crystalline sodium aluminosilicate thus formed being then washed and dried.
This process, with such a gel composition, even though being suitable for producing zeolite P on a bench scale, can't always be directly transposed to industrial scale.
In EP-A-565,364 is disclosed a process for industrial production of P zeolite having the oxide formula EQU M.sub.2/n, Al.sub.2 O.sub.3, (1.8-2.66)(preferably 1.90-2.10)SiO.sub.2, yH.sub.2 O
wherein y is the water content, comprising the steps of:
i. a sodium aluminate solution having a temperature of at least 25.degree. C. is mixed with a sodium silicate solution at a temperature of at least 25.degree. C. in a stirred vessel in the presence of a slurry of P zeolite seed to form a gel having the composition, Al.sub.2 O.sub.3 :(1-3.5)(preferably 1.80-2.2)SiO.sub.2 :(1.2-7.5) (preferably 1.5-5)Na.sub.2 O: (25 to 450) (preferably 40 to 150) H.sub.2 O PA1 ii. ageing the gel at a temperature above about 25.degree. C. with stirring to maintain solids in suspension for a period of least about 0.1 hour, and PA1 iii. separating the P zeolite product, washing and drying. PA1 i. The form of the zeolite which was produced was established using standard XRD method. PA1 x being at least 1.8 PA1 y being the water content, PA1 wherein a sodium silicate solution and a sodium aluminate solution are continuously added together in a first reacting zone in the presence of zeolite P seeds, to produce a mixture having the general formula: EQU 3.0-5.0Na.sub.2 O, 2.2-7.5SiO.sub.2, Al.sub.2 O.sub.3, 75-450H.sub.2 O
Even though satisfactory, this process is a batch process and there is therefore a need for a continuous process for the production of zeolite P.